This invention relates to a disc cartridge housing for a disc-shaped recording medium, such as an optical disc or a magneto-optical disc. More particularly, it relates to a method and apparatus for molding a disc cartridge having means for preventing the disc-shaped recording medium from being damaged at an edge portion of a head-accessing opening. The disc-shaped recording medium is referred to herein collectively as an optical disc.
The optical disc is a recording medium capable of recording or having recorded thereon desired information signals, such as speech or picture signals, with a high recording density. The optical disc is housed for rotation in a cartridge main body to form a disc cartridge. The optical disc having a diameter of not more than 64 mm is capable of recording speech signals continuing for 74 minutes, while the main cartridge body is of an extremely small size, its diameter being as small as 6 mm.
When the disc cartridge is loaded on the recording/reproducing apparatus, the optical disc has its center portion loaded on a disc rotating driving unit so that it is driven at a high rpm. While the optical disc housed within the disc cartridge is run in rotation, a laser beam is radiated from an optical pickup mounted on the recording/reproducing apparatus to the disc for reproducing information signals recorded on an information signal recording area formed on the major surface of the disc. On the other hand, while a laser beam radiated from the optical pickup is illuminated on an information signal recording area of e.g., a magneto-optical disc, as a recordable optical disc, an external magnetic field modulated by an external magnetic field generating device in accordance with information signals to be recorded is applied for recording desired information signals.
Referring to FIGS. 1 and 2, a cartridge main body 100 is constituted by an upper cartridge or part 101 and a lower cartridge or part 102, both being in the shape of shallow saucers, and an optical disc 1 rotatably housed within the cartridge main body 100. That is, the upper and lower cartridge halves 101, 102 are formed with peripheral upstanding wall sections, annular wall sections, not shown, formed on the inner surfaces for being abutted against each other for defining a housing space for the optical disc 1, and with plural engagement protrusions. The upper cartridge half 101 and the lower cartridge half 102 are assembled together by abutting the upstanding peripheral wall sections and the annular wall sections to one another and welding by an ultrasonic welder, not shown, for constituting the thin box-shaped cartridge main body 100.
For unifying the upper and lower cartridge halves 101, 102 together, ultrasonic waves are applied from an ultrasonic welder applied to the lower cartridge half 102 to the fitting protrusions on the inner surfaces or upstanding peripheral or annular wall sections formed on the inner surfaces, with the protrusions or the wall sections being oscillated and locally heated and fused so as to be fused together on terminating the impression of the ultrasonic waves.
The mid portion of the lower cartridge half 102 constituting the cartridge main body 100 is formed with a circular opening operating as an opening for permitting intrusion of a disc table 120 therein on loading the disc cartridge in the recording/reproducing apparatus, as shown in FIG. 2. The disc table 120 is mounted on the recording/reproducing apparatus and operates for running the optical disc 1 in rotation. Specifically, the opening for insertion of the disc table 120 exposes to the outside a magnet-clamping hub 4 which is provided for closing a center opening of the optical disc 1.
The disc table 120 has a center spindle shaft 121 for passing through the center of the disc table from the lower side to the upper side, and a annular magnet 122 around the spindle shaft 121. The disc table 120, intruded via the disc table intrusion opening formed in the lower cartridge half 102, is engaged in a spindle shaft opening formed in the hub 4, and attracts and holds the hub 4 by the magnet 122 for holding the disc cartridge.
The upper and lower cartridge halves 101, 102, making up the cartridge main body 100 are formed with rectangular-shaped head-accessing openings 103 (FIG. 3 et seq.) exemplified by openings 103A, 103B(FIGS. 1 and 2), respectively, in register with each other. These rectangular-shaped openings 103A, 103B are formed for exposing portions of the information recording area on the major surface of the disc 1 rotatably housed within the cartridge main body 100 to the outside and permit intrusion therein of an optical pickup mounted on the recording/reproducing apparatus. These head-accessing apertures 103 are formed as rectangular-shaped openings extending from a mid portion in the transverse side of the cartridge main body 100 as far as a portion proximate to the opening for intrusion of the disc table.
A U-shaped shutter member, not shown, for opening/closing the head accessing apertures 103, is mounted on the disc cartridge. The shutter member usually closes either head accessing aperture 103 under the force of resiliency of a shutter spring, not shown, for preventing intrusion and deposition of dust and dirt in the inside of the disc cartridge via either head accessing aperture 103. When loaded on the recording/reproducing apparatus, the shutter member is moved by a shutter opening member to a second position opening the head accessing aperture 103. To this end, the shutter opening member is mounted on the recording/reproducing apparatus for being engaged with a shutter opening guide groove, not shown, formed in the front side of the cartridge main body 100.
The upper and lower cartridge halves 101, 102 making up the cartridge main body 100 of the disc cartridge are molded by injecting a molten synthetic resin material into a cavity of a die device. The die device is roughly made up of a movable die 130 (FIGS. 3 and 5) defining a cavity for the inner side of the cartridge half 101 or 102 and a stationary die 131 towards and from which the movable die 130 is moved with a die closing and die opening movement for defining a cavity for the front side of the cartridge half 101 or 102, as shown in FIG. 3. For defining the head-accessing aperture 103, the die device also includes an insert die (auxiliary die) 132 which is built in the movable die 130 for being abutted against the stationary die 131 during die closure for defining the cavity for the head-accessing aperture 103.
The inner surfaces of the upper and lower cartridge halves 101, 102 facing each other are likely to make contact with the optical disc 1 rotatably contained in the cartridge main body 100. Thus the surface of the movable metal mold 130 of the die device is ground for improving surface smoothness of the inner surfaces of the upper and lower cartridge halves 101. The die device is configured for arcuately chamfering the opening edge of the head-accessing aperture 103 for preventing the surface of the optical disc 1 from being damaged by being chafed against the opening edge of the aperture 103. With the present die device, for chamfering the opening edge portion of the head-accessing aperture 103, a chamfered portion 104 is formed at the proximal end of a protruding portion of the auxiliary die 132 designed to form a cavity for forming the head-accessing aperture, and die matching is achieved at this chamfered portion 104.
One of the problems encountered in injection molding is that burrs tend to be produced on the registration surfaces of the dies due to tolerances or abrasion of the dies, and that, since the registration surfaces of the movable die and the auxiliary die are positioned on the inner surfaces of the upper and lower halves 101, 102, the burrs produced on the inner surfaces of the upper and lower cartridge halves tend to damage the major surface of the optical disc.
For overcoming such deficiency, it may be envisaged to employ a die device made up of a movable die 140 having a cavity-defining protrusion on its major surface for defining a head-accessing aperture 103, and a stationary die 141, as shown in FIG. 4. With such die device, the cavity-defining protrusion of the movable die 140 defining the head-accessing aperture 103 is abutted against the stationary die 141.
This die device suffers from an inconvenience that it is extremely difficult to register the movable die 140 with respect to the stationary die 141 in a region of the head-accessing aperture 103 during mold closure. The die device also suffers from a drawback that a grinder mechanism is likely to be abutted against the cavity-forming protrusion to render it difficult to grind the surface of the stationary die 140. Consequently, this type of the die device is scarcely put to practical utilization and hence a die device having the auxiliary die as described above is generally employed.
However, the above-described die device employing the insert die suffers from the phenomenon of sagging of the surface end portion of the ground movable die towards the die matching surface with the insert die 132 as a result of grinding, as shown in FIG. 5. This phenomenon occurs on the surface of the movable metal mold 130 to a depth of approximately 10 to 30 .mu.m depending on the grinding tolerance. The result is that burrs 105 are produced on the inner surface along the opening edge 104 of the head-accessing opening 103, as shown in FIG. 6.
These burrs 105 raise a problem that, during the time when the upper and lower cartridge halves 101, 102 ape ultrasonically welded to each other or when the disc cartridge is being chucked to the disc table 120, the burrs 105 tend to be contacted with the optical disc 1 to mar its surface, as shown in FIG. 7.
That is, during ultrasonic welding of the upper and lower cartridge halves 101, 102, the optical disc 1 housed within the cartridge main body 100 is vibrated within the inside of the cartridge main body 100 under impressed ultrasonic waves, so that its surface is caused to impinge strongly on the surfaces of the upper and lower cartridge halves 101, 102. In such case, the optical disc 1 tends to be vibrated in an inclined position within the inside of the cartridge main body 100 so that its major surface is caused to bear against the opening edge 104 of the head-accessing aperture 103. Since the burrs 105 are occasionally produced on the opening edge 104 of the head-accessing aperture 103, the surface of the optical disc 1 tends to be injured by these burrs 105.
During chucking of the disc cartridge, the disc table 120 is intruded via the disc-intrusion opening into the interior of the cartridge main body 100. However, since the optical disc 1 is not positioned accurately within the cartridge main body 100, there are occasions wherein the spindle shaft 121 thrusts the optical disc 1 towards the upper half 101 via the hub 4. 0f course, the optical disc 1 is subsequently chucked in the regular manner by the spindle shaft 121 engaging in the spindle shaft opening of the hub 4, as shown in FIG. 2.
If the optical disc 1 is thrust by the spindle shaft 121, there are occasions wherein the optical disc 1 is thrust in a tilted state in the interior of the cartridge main body 100 such that the major surface of the optical disc 1 is caused to bear against the opening edge 104 of the head-accessing opening 103, as shown in FIG. 1. Since the burrs 105 tend to be produced on the opening edge 104 of the head-accessing aperture 103, the surface of the optical disc 1 tends to be marred by these burrs 105.